1/* Initialization of uninitialized regs.
2   Copyright (C) 2007, 2008, 2009 Free Software Foundation, Inc.
3
4This file is part of GCC.
5
6GCC is free software; you can redistribute it and/or modify it under
7the terms of the GNU General Public License as published by the Free
8Software Foundation; either version 3, or (at your option) any later
9version.
10
11GCC is distributed in the hope that it will be useful, but WITHOUT ANY
12WARRANTY; without even the implied warranty of MERCHANTABILITY or
13FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14for more details.
15
16You should have received a copy of the GNU General Public License
17along with GCC; see the file COPYING3.  If not see
18<http://www.gnu.org/licenses/>.  */
19
20#include "config.h"
21#include "system.h"
22#include "coretypes.h"
23#include "tm.h"
24#include "tree.h"
25#include "rtl.h"
26#include "regs.h"
27#include "expr.h"
28#include "tree-pass.h"
29#include "basic-block.h"
30#include "flags.h"
31#include "df.h"
32
33/* Check all of the uses of pseudo variables.  If any use that is MUST
34   uninitialized, add a store of 0 immediately before it.  For
35   subregs, this makes combine happy.  For full word regs, this makes
36   other optimizations, like the register allocator and the reg-stack
37   happy as well as papers over some problems on the arm and other
38   processors where certain isa constraints cannot be handled by gcc.
39   These are of the form where two operands to an insn my not be the
40   same.  The ra will only make them the same if they do not
41   interfere, and this can only happen if one is not initialized.
42
43   There is also the unfortunate consequence that this may mask some
44   buggy programs where people forget to initialize stack variable.
45   Any programmer with half a brain would look at the uninitialized
46   variable warnings.  */
47
48static void
49initialize_uninitialized_regs (void)
50{
51  basic_block bb;
52  bitmap already_genned = BITMAP_ALLOC (NULL);
53
54  if (optimize == 1)
55    {
56      df_live_add_problem ();
57      df_live_set_all_dirty ();
58    }
59
60  df_analyze ();
61
62  FOR_EACH_BB (bb)
63    {
64      rtx insn;
65      bitmap lr = DF_LR_IN (bb);
66      bitmap ur = DF_LIVE_IN (bb);
67      bitmap_clear (already_genned);
68
69      FOR_BB_INSNS (bb, insn)
70	{
71	  unsigned int uid = INSN_UID (insn);
72	  df_ref *use_rec;
73	  if (!NONDEBUG_INSN_P (insn))
74	    continue;
75
76	  for (use_rec = DF_INSN_UID_USES (uid); *use_rec; use_rec++)
77	    {
78	      df_ref use = *use_rec;
79	      unsigned int regno = DF_REF_REGNO (use);
80
81	      /* Only do this for the pseudos.  */
82	      if (regno < FIRST_PSEUDO_REGISTER)
83		continue;
84
85	      /* Do not generate multiple moves for the same regno.
86		 This is common for sequences of subreg operations.
87		 They would be deleted during combine but there is no
88		 reason to churn the system.  */
89	      if (bitmap_bit_p (already_genned, regno))
90		continue;
91
92	      /* A use is MUST uninitialized if it reaches the top of
93		 the block from the inside of the block (the lr test)
94		 and no def for it reaches the top of the block from
95		 outside of the block (the ur test).  */
96	      if (bitmap_bit_p (lr, regno)
97		  && (!bitmap_bit_p (ur, regno)))
98		{
99		  rtx move_insn;
100		  rtx reg = DF_REF_REAL_REG (use);
101
102		  bitmap_set_bit (already_genned, regno);
103
104		  start_sequence ();
105		  emit_move_insn (reg, CONST0_RTX (GET_MODE (reg)));
106		  move_insn = get_insns ();
107		  end_sequence ();
108		  emit_insn_before (move_insn, insn);
109		  if (dump_file)
110		    fprintf (dump_file,
111			     "adding initialization in %s of reg %d at in block %d for insn %d.\n",
112			     current_function_name (), regno, bb->index, uid);
113		}
114	    }
115	}
116    }
117
118  if (optimize == 1)
119    {
120      if (dump_file)
121	df_dump (dump_file);
122      df_remove_problem (df_live);
123    }
124
125  BITMAP_FREE (already_genned);
126}
127
128static bool
129gate_initialize_regs (void)
130{
131  return optimize > 0;
132}
133
134static unsigned int
135rest_of_handle_initialize_regs (void)
136{
137  initialize_uninitialized_regs ();
138  return 0;
139}
140
141struct rtl_opt_pass pass_initialize_regs =
142{
143 {
144  RTL_PASS,
145  "init-regs",                          /* name */
146  gate_initialize_regs,                 /* gate */
147  rest_of_handle_initialize_regs,       /* execute */
148  NULL,                                 /* sub */
149  NULL,                                 /* next */
150  0,                                    /* static_pass_number */
151  TV_NONE,                              /* tv_id */
152  0,                                    /* properties_required */
153  0,                                    /* properties_provided */
154  0,                                    /* properties_destroyed */
155  0,                                    /* todo_flags_start */
156  TODO_dump_func |
157  TODO_df_finish                        /* todo_flags_finish */
158 }
159};
160